Abstract: Seeking for hypoxia imaging agents with simple structure and good performance, 3 methyl 3 N (2 hydroxyethyl) 2 butanone oxime (EtAO) is synthesized and labeled with 99 Tc m. In vitro and in vivo evaluation of this complex as a tumor hypoxia marker is performed and the result is compared with that of 99 Tc m Bn(AO) 2, a putative hypoxic tracer. The cell experiments show that 99 Tc m EtAO has hypoxia affinity as well as 99 Tc m Bn(AO) 2. The biodistribution in tumor bearing mice indicates that 99 Tc m EtAO can concentrate selectively in tumor tissues. As a potential hypoxia imaging agent, 99 Tc m EtAO has the value for the further investigation.